Oil composition for air



United States Patent OIL COMPOSITION FOR AIR FILTERS Charles E. Paxton,Jamesburg, N. 1., assignor to Esso Research and Engineering Company, acorporation of Delaware No Drawing. Application February 11, 1952,Serial No. 271,079

7 Claims. 01. 260 -23 The present invention relates to an improved oilcomposition for air filters and particularly to a mineral oil containingan improved combination of tackiness or adhesive agents by which itadheres properly to the strands or fibres, etc., of an air filter orequivalent device and also picks up and holds dust and other foreignmatter coming in contact therewith.

In the prior art it has been the practice for some time to dip airfilters, such as are used in airstraining or conditioning apparatus andthe like, containing stranded, matted, or fibrous material, into oil oroily material to improve their dust adsorptive or dust holding capacity.Such filters, as is well known, are usually and primarily composed of amat of fibres arranged criss-cross and miscellaneously so that airpassing through the filter must move in a devious path. By the use of anadherent film of oil, or the like, the dust particles entrained in theair are extracted and held by the filter fibres. Such filters are widelyused in space heating systems, air conditioning systems, in the intakesof refrigeration apparatus and various types of internal combustionengines, as well as in many other locations and installations. Theconditions of temperature, air velocity, etc., vary widely for dilferentinstallations. 'One particular installation where difficulty has beenencountered in obtaining an oil of optimum tackiness, or adhesivequalities, is in the intake air filters of diesel locomotives. Diesellocomotives are driven by internal combustion engines of relativelylarge horsepower and large air requirements. It has been the practice inthe past to provide such locomotives with a fibrous type filter which isdipped in a mineral base oil, usually an oil of lubricating grade andviscosity. Such oils tend largely to drip oil the filter, especially atthe relatively elevated operating temperatures of diesel locomotiveengines. This tendency may be less pronounced in other filters where airis filtered at less elevated temperatures, but it exists to a greater orlesser degree in all types of oil treated fibrous filter media.

A major purpose of the present invention is the modification of thefilter oil to improve its adherence to the fibrous structure and also toenhance its capacity to take up dust from the air whichpasses throughit. This is accomplished by the use of what now appears to be an optimumcombination of a conventional tackiness agent, such as stringy liquidpolymer, e. g. a hydrocarbon of the elastomer type, in combination witha small amount of an alkali metal soap.

Specifically, a preferred form of the invention involves a mineral oilof appropriate grade and viscosity containing, about 1 to 5% of ahydrocarbon polymer, e. g. a polymer of isobutylene or a copolymer ofisobutylene and which contained no soap.

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. 2 styrene. To this is added from 0.1 to 2% by weight, or preferablyabout 0.25 to about 0.5%, of an alkali metal soap, such as a stearate,preferably lithium stearate, although sodium stearate or the soaps ofclosely related fatty acids may also be used in some cases.

A series of tests were made to determine the optimum tackiness agentsfor the peculiar purposes of the present invention. It was found thatlithium stearate is considerably superior to the other soaps tested whenused in combination with a tacky polymer, e. g. about 2% of an oilsolution of isobutylene polymer of medium molecular weight, i. e. ofabout 50,000 to 100,000. Sodium stearate was considerably less effectivewith this polymer. Aluminum stearate was much less effective than thesodium stearate. The difference is so great that lithium stearate or thelithium soaps of other fatty acids near the C18 range appear to besuperior to an unexpected degree over the other soaps. As indicatedabove, sodium stearate has some efiect. The other metal stearates arerelatively quite useless. The invention will be more clearly understoodby reference to the following examples.

Example I A mineral base lubricating oil of about S. S. U. viscosity at210 F. was combined with 2% by weight of a viscous polymeric oiladditive. This additive consists of a mineral oil of lubricating gradecontaining 8 to 10% by weight of an isobutylene polymer of about 60,000to 100,000 molecular weight. This additive is commonly used as atackiness agent in lubricating oils, gear oils and the like. Thiscomposition, containing about 0.16 to 0.2% of the polymer per se wastested for its adhesion to an air filter at temperatures respectively ofF., and 200 F. It was also tested for adhesion at the same temperaturesby coating it on a 2 x 4 inch smooth metal panel, measuring themilligrams of oil which adhered to the metal after it had beenconditioned to a constant weight, i. e. so that no further oil drainedaway.

In the above tests the mineral oil plus 2% of the tacky polymer solutionshowed an adherence of 10.5 milligrams of oil per square inch on themetal panel at-125 F. At

Example 11 (a) (b) The composition of Example I was combined withvarious proportions of difierent soaps to determine their effect onadhesion to the metal and to the air filter respectively. (a) With 0.5%aluminum stearate, adherence at 200 F. to the metal panel was 8.5milligrams per square inch, slightly more than the composition ofExample I (b) This increased to 11.1 milligrams with 1% sodium stearate,a very slight improvement over Example I. Both of these values wereconsidered quite low, although the sodium stearate showed some utility.

Example 111 The composition of Example I was modified by adding 0.5% byweight of the lithium stearate. This showed a remarkable increase inadhesivity both to the metal and to the air filters. At 125 F. 49.3milligrams of oil adhered to each square inch of the metal panel, thisbeing reduced to 26.2 milligrams at 200 F. On the air filters, 126.3grams adhered at 125 F., about 3 /2 times as much adhered when thelithium soap was not used. At 200 F 110.6 grams still adhered to thefilters, only a moderate of polymer per se) appears to be about optimum.From inspection, it is apparent that other tacky polymers such asstybutene (styrene-polyisobutylene) and Butyl or natural rubber polymersor copolymers, broken down to reduction from the amount which adhered at125 F., and 5 a proper molecular weight for high tackiness, may be morethan seven times as much as was retained in EX- substituted forpolyisobutylene, so long as they are of ample Since the uantity of soapused was very small, appropriate, i. e. medium molecular weight (e. g.25,000 t 1 s evldent that lithlum stearate has an outstanding effect to125,000, preferably 60,000 to 100,000) so as to conm lmprovmg theadhesion of the oil. fer a good degree of tackiness on the oil. Theproportions Example IV of additives may be varied somewhat more widelyif desired, e. g. 0.1 to 2% of soap and 0.05 to 1% of polymer Order 9detelmlne efiect of P $6, the (0.4 to 10% of the conventional polymersolution in oil), same base m1neral o1l used 1n Example I was combined fsome purposes. with 0.5% by welght of lithium stearate. It adhered Thecapacity f the filt to k up dust f air passquit? to t mFtal Panel at p W50 devoid ing therethrough is approximately in direct proportion f a k lfh It had 0 Partlcular utlllty as a filter to the amount of oil whichadheres to the filter. It is coa-tmg mgdmmevident that the use of asmall amount of the tacky E l V (a) (b) polymer and a very small amountof the lithium stearate Th effects a remarkable improvement.

(a) e same 011 as m.EXamp1e I IV was It Will be understood, of course,that oils of various 62;? with by wslght of hthmm steara'fe- Atviscosities may be used and that the proportion of the 2 mflhgram-Sadhered to each Square Inch of respective additives may be varieddepending somewhat i f (b) when 1% of the tacky PPlymer upon thefineness of the fibres of which the filter is comsohitlon dcscnbed iadded the quafilty posed and depending even more on the temperaturerange henngfo metal Increase? to mmgrams' at which the filter is to beused. It will be understood, of What 18 more slgmficant however 15 thefact that the course, that the oils employed may have otherconstituents, adherent fibre i very much tat/kit hence although, ingeneral, those described above appear to be much more effective as adust holdmg medium. about p Example VI What is claimed is: 1. A tackyoil composition for coating air filters and gf (i z i i i gi i the likeconsisting essentially of a mineral oil of lubriz g z g i 0 g 8 m beating grade and viscosity containing about 0.05 to 1% v vas quite eflfetiie 7l 5 g r aiiz oi il b ein g li elii as co; of a tacky elastomerPolymer of 25000 to 12500O molecf 'd pared wlth 1105 of Exampla In at F.girl) welght and about 0 l to 0 5% of a lithium atty aci Example VII 2.An oil composition for coating the fibrous air filter Example I wasrepeated, using, however, 4% of the 8 l a g fi i g z gg gi g igpolyisobutylene solution instead of 2%. In the metal of u gd an g ly con3 f 5 g ht panel test only 9.9. milligrams adhered per square inch at 9y wear on PO ymer m e 40 w1th1n the range of about 25,000 to 125,000,and about 125 F. The proportion of polymer used seems to make 1 Y 57 f ff tt I Cid of a roxi no significant diiierence in adhesion to the metal.9 o a If]. 5 5; 3.) a 5 PP I Apparently the polymer is required to givethe oil the matelY C 8 census.-. h th necessary tacky quality to pick upand hold the dust pargzomposltlon ordin 0 .8.1 1 W 6116111 5011p ticles,The soap, on the other hand, seems to be essential 1S llthlum ff tocause the composition to adhere and not drain away p 1 according toclaim 2 h r n h s p from the supporting fibres of the filter. 1s lithiumoleate.

The above data are tabulated as follows: 5. An oil composltlon for ngfibrous arr filter FILTER OIL CHARACTERISTICS Metal Panel Filter Adhe-Test, mg./ sio n, gdfilte r, Composition 7 x7 Taokiness 125 F. 200 F.125 F. 200F.

Oil, S. 8. U. vis. 210 F. (No addl- 9. 4 Light tackitlve). ness. Ex.I.2% Poly. s01 36. 6 16. 9 Tac y- Ex. II (tn-0.6% Al. Stear Non-Tacky.EX. II (ID-0.5% Na. Steer D0. Ex. III-2%Poly. So1.+0.5% Li stearate.126.3 110.6 Tacky. Ex. IV.O.5% Li. Stear Non-Tacky. Ex. V (a)-0.25% Li.Stear Do. Ex y (IQ-10.25% Li. Stear.+1% Poly Tacky- Ex. vr2% Poly. s01.+05% Li. Oleata. 71.5 Do. Ex. VII-11% Poly. S01 9. 9 Do.

The blanks in the table indicate that tests were not and the likeconsisting essentially of a mineral base oil made, being consideredunnecessary in view of the data of lubricating grade and viscosityhaving a viscosity beobtained. tween about 35 and 100 S. S. U. at 210 F.and con.-

From the foregoing, it appears that it is desirable to use taining about0.08 to 0.2% by weight of a viscous hydrothe soap, preferably oflithium, to hold the oil on the 70 carbon polymer having a molecularweight within the filter and to use the polymer solution additive tohold dust to the oil film. Neither ingredient by itself addsparticularly to the performance over that of straight mineral oil. Acomposition having 0.25 to 0.5 lithium soap and 1 range of 25,000, to125,000, and about 0.5% by weight of lithium stearate.

6 Composition according to claim 5 wherein the polymer ispolyi'sobutylene, of molecular weight within the to 2% of the 8 to 10%polymer solution (0.08 to 0.2% range of about 60,000 to 100,000.

7. A tacky oil composition having the property of adhering to fibrousfilter media and the like and having a tacky surface characteristic suchas to retain dust particles coming in contact therewith, comprising amineral oil of lubricating grade and viscosity, a lithium soap inproportions of 0.25 to 0.5% by weight, based on the total composition,and 0.08 to 0.2% of a viscous tacky polyisobutylene of 25,000 to 125,000molecular weight.

References Cited in the the of this patent UNITED STATES PATENTSKlemgard Nov. 6, 1934 Stafford July 5, 1938 Mueller Cunradi July 19,1938 Simpson Feb. 7, 1939 Morgan Jan. 29, 1946 Davis et a1 Nov. 16, 1948Morway Dec. 13, 1949 Moore Aug. 11, 1953

7. A TACKY OIL COMPOSITION HAVING THE PROPERTY OF ADHERING TO FIBROUS FILTER MEDIA AND THE LIKE AND HAVING A TACKY SURFACE CHARACTERISTIC SUCH AS TO RETAIN DUST PARTICLES COMING IN CONTACT THEREWITH, COMPRISING A MINERAL OIL OF LUBRICATING GRADE AND VISCOSITY, A LITHIUM SOAP IN PROPORTIONS OF 0.25 TO 0.5% BY WEIGHT, BASED ON THE TOTAL COMPOSITION, AND 0.08 TO 0.2% OF A VISCOUS TACKY POLYISOBUTYLENE OF 25,000 TO 125,000 MOLECULAR WEIGHT. 